Surveyor s combined protractor and scale



N. WILSON. Surveyors' Combined Pro-tractor and Scale.

N o. 224,811.v l Patented Feb. 24,1880.

m... m lllnllr 1o uated guide-arm removably y i UNITED STATES PATENT OFFICE.

NATHANIEL WILSON, OE OH'ILLIOOTHE, OHIO.

suRvEYoRs COMBINED PROTRACTOR AND SCALE.

SPECIFICATION forming part of Letters Patent No. 224,811, dated February 24, 1880.

Application filed April 25, 1879.

' of Chillicothe, in the county of Ross and State of Ohio, have invented a new and useful Instrument called Surveyors Combined Protractor and Scale, which is fully described in the following specification.

My invention relates to improvements in protractors; and it consists in making a gradattached to the diameter-bar of the inner circle of the protractor, and provided with shouldered end extensions, which pass over the outer and in ner circles ofthe protractor.

In the drawings, Figure 1 is a plan view of myinvention. Fig. 2 is a side elevation. Fig. 3 is a vertical section. Fig. 4 is a section on the line z z, Fig. 1, showing the beveled edge of the under side of the removable guide-arm.

zo Fig. 5 is a section on the lineyy, showing the guide-arm extending over the outer and inner circles.

My protractor is formed by uniting two concentric circles of brass, nickel, or other suitable material by rivets or other means, an

annular ring, Dwhose.width is less than that of the circles being interposed between them, thus forming an annular groove within the interior circumference of the circle for the ac- 3o commodation of an inner circle, F.

On the rim of the outer circle, which may be of any convenient width, are marked the degrees of the quadrant, beginning with zero (0) and counting ninetydcgrees to the E. or

3 5 W. points.

A guide armor bar, R, graduated to linear measurement, such as feet, rods, poles, &c., is removably attached to and moves with the diameter-arm of the inner circle. It may be 4o secured to said arm in any convenient way.

The ends of the guide-arm are extended so as" to formv guide-flanges P, which `may be graduated and provided with a micrometerscale. These flanges project a sufficient distance beyond the outer edge of the outer circle to give direction to a course or line which extends beyond the limits of the circles, so that by simply sliding `the instrument along the course or line thus prolonged we may pre- `the outer circle, and a line serve and complete the measurement of the true course.

The inner face ot' the guide-arm is beveled and the under face is also beveled, and is extended below the diameter-arm, so that it rests clear of the inner circle and diameterarm, but directly on the paper, and thus gives a true and accurate bearing for a'right-line pen, pencil, or picker point. Where the guide arm passes over the circle it is provided with shoulders, which form recesses or grooves for the passage ofthe circles.

By making the guide-arm removable it can be replaced by a new one without putting in a new inner circle, as required in the present form of protractors, when the beveled vedge of the guide-arm becomes indented, rough, &c.

An arm, N extends from the diameter-arm to the opposite side of the inner circle and gives stability to the component parts. It is provided with a handle or knob, K, for revolving the inner circle and guide-arm.

The method of plotting is as follows: First adjust the instrument so that the straightedge of the guide-arm stands directly `over the north and south points of the outer circle and the center A of the startingpoint. For instance, the calls of a survey are forty poles north, thence twenty poles north forty degrees east, 8vo., the instrument is placed upon the paper, and, com.- mencing at the center or starting-point, a line is drawn by the guide-arm, which serves as a rule, forty poles north by the scale. The instrument is then, without any alteration of its relative points, moved or caused to slide over the paper until the center A is over the terminal point of the line. The inner circle is then revolved until the flange of the guidearm marks forty degrees east on the scale of poles on the scale is drawn. The same operation is repeated untilthe calls are complied with and the starting-point reached, thereby accomplishing in a simple and easy manner with this instrument what has4 heretofore, under lthe ordinary methods, required several instruments and much time, care, and labor.

Having thus described my invention, what showing twenty I claim, and desire to secure by Letters Patanges l?, extending over the inner and'outer ent, is circles, substantially as described, and for the In aprotraetor, the combination of an outer purpose set forth. eirole graduated to degrees, an inner circle NATHANIEL WILSON. 5 having one or more diameter-arms, With a de- Attest:

taehable guide-arm, R, graduated to linear W. E. EVANS,

measurement, and provided With shouldered I C. T. CARRIER. 

